1. Field of the Invention
The present invention relates to a computed tomography unit, having a radiation detector and an X-ray source. The invention also relates to a method for operating a computed tomography unit of this type.
2. Description of the Prior Art
A computed tomography unit of the type described above has an X-ray source which directs a pyramid-shaped X-ray beam through an object under examination, for example a patient, onto a radiation detector. The X-ray source and, depending on the design of the computed tomography unit, also the radiation detector are arranged, on a gantry which is able to rotate around the patient. The patient can lie on a table which can be shifted or moved along a system axis relative to the gantry. In this way it is possible, inter alia, to helically scan a region of the patient""s body, so that a volume of the patient""s body being scanned during the scan. Sectional images of planar layers or slices of the patient""s body are reconstructed from the measured values obtained. If the gantry does not rotate during a scan, but rather the table is simply moved along the system axis, it is possible to compile an overview image (topogram) of the patient.
To assign a region of the patient""s body to sectional images or to an overview image obtained by means of the scan, a treating physician can orient himself or herself from, for example, features known as anatomical land marks, which can be seen both in the sectional image or the overview pictures and on the patient. Orientation by means of a laser sight which may be present in front of the gantry also is possible. A laser sight of this type is described, for example, in U.S. Pat. No. 6,041,249.
A drawback of these methods, however, is the inaccuracy and difficulty in assigning a particular sectional image to the corresponding region of the patient""s body.
An object of the present invention is to provide a computed tomography unit of the type initially described with which it is easier to assign a sectional image or an overview picture to a corresponding region of a patient""s body. A further object of the invention is to provide a method for operating a computed tomography unit of this type which facilitates this object.
According to the invention, the first object is achieved in a computed tomography unit, having a radiation detector and a X-ray source, which in order to scan an object under examination emits a pyramid-shaped X-ray beam, which penetrates through the object under examination, and wherein the computed tomography unit has an optical recording device which, during the scanning, records optical images of a partial surface, which faces the X-ray source and through which the pyramid-shaped X-ray beam has penetrated, of the object under examination. In this way, for example after a patient has been scanned, the optical images can be compared with tomographs or overview images obtained by means of the scan, and this can advantageously be utilized to assign in particular sectional images to the regions of the patient""s body.
In an embodiment of the invention, the optical recording device is arranged on a rotating part of the gantry of the computed tomography unit, and given a suitable arrangement of the optical recording device on the gantry, conditions are established which enable the optical recording device always to be oriented in a defined position relative to the X-ray source and in particular onto the partial surface of the patient through which the X-ray beam penetrates during the recording of a computed tomograph.
In an embodiment of the invention, the optical recording device has at least one charge-coupled device (CCD) linear array.
In a variant of this embodiment, the optical recording device has an automatic focusing device, allowing sharply defined optical images to be obtained.
In a further embodiment, the optical images are processed further by a signal-processing unit. Therefore, it is possible to electronically assign the sectional images or overview pictures obtained by means of the scan to the regions of the object under examination.
The other object of the invention is achieved in a method for operating a computed tomography unit, having a radiation detector and an X-ray source, which in order to scan an object under investigation emits a pyramid-shaped X-ray beam, which penetrates through the object under examination, the computed tomography unit having an optical recording device which, during the scanning, records optical images of a partial surface, which faces the X-ray source and through which the pyramid-shaped X-ray beam has penetrated, of the object under examination, having the following method steps:
a) recording an optical image at each scanning step,
b) constructing an image of a surface of the object under examination from optical images of the partial surfaces which have been penetrated by the pyramid-shaped X-ray beam during the scanning, and
c) assigning the image to a sectional image obtained by means of the scan or an overview picture (topogram).
This allows the image of the surface to be compared with the sectional images or overview images after a scan and, in particular, allow regions of an examined patient""s body to be assigned to sectional images.
In another embodiment of the invention, a signal-processing unit constructs the image of the surface of the object under examination. Consequently, it is possible to electronically assign the sectional images or the overview picture to the regions of the object under examination.